The term "cocktail-party effect" refers to the human ability of listening to a conversation in an acoustic environment in which several persons are talking simultaneously. This ability is known to often become impaired in aging, thereby causing an elderly person to withdraw from society at an age when he/she could still have much to contribute. Efforts to alleviate this impairment have been impeded by the fact that neither its precise characteristics in the young, nor the causes of its breakdown in the old, are currently understood. The objective of the proposed research is (1) to assess speech perception in speech noise by elderly listeners and relate this ability to a comprehensive auditory performance profile, (2) to compare speech perception performance in speech noise by elderly and young listeners having either normal or impaired hearing, and (3) to investigate auditory resolution of, and selective attention to, signals separated in space or mixed in the same channel, both in elderly and in young listeners. Part of the objectives require testing a large number of elderly subjects, whereas another part necessitates testing a small number of young, normal subjects over a long period of time. The objectives will be achieved by using standard and newly developed audiological tests as well as standard psychophysical techniques. Assessment of spatial hearing will be accomplished in simulated free field. Characterization of the auditory performance profile of the various subject groups will be based on advanced statistical analysis techniques. The major socio-medical significance of the proposed study lies in that it is directed toward a wide-spread impairment of verbal communication in the elderly. Its clinical significance lies in that it will attempt to differentiate between peripheral and central components of the impairment. Its scientific relevance consists (1) of determining the place of the "cocktail-party effect" in an overall picture of audiological, psychophysical, and cognitive abilities, and (2) of characterizing some of the most important psychoacoustic and cognitive components of the phenomenon.